Chip level power reduction using encoded communications

ABSTRACT

A circuit arrangement, method, and program product communicate data over a communication bus by selectively encoding data values queued for communication over the communication bus based at least in part on at least one data value queued to be communicated thereafter and at least one previously communicated encoded data value to reduce bit transitions for communication of the encoded data values. By reducing bit transitions in the data communicated over the communication bus, power consumption by the communication bus is likewise reduced.

FIELD OF THE INVENTION

The invention is generally related to data processing in a computingsystem including a plurality of interconnected processing blocks (i.e.,nodes), and in particular to processor architectures and communicationarchitectures incorporated therein.

BACKGROUND

A network on a chip (NOC) is a novel integrated circuit architecturethat applies a network-based architecture to a single chip to create aunique processing unit. A typical NOC includes a plurality of integratedprocessor (IP) blocks coupled to one another via the network. NOCprocessing units typically distribute (i.e., allocate) various parts ofa job to different hardware threads of one or more IP blocks to beexecuted by the one or more IP blocks in the NOC processing unit, wherethe distribution typically includes transmitting data packets includingone or more data words between one or more hardware threads of the NOC.With the number of IP blocks in the standard computer systems expectedto rise, efficiently handling workload distribution has becomeincreasingly demanding.

In many conventional NOC architecture systems, data packets are oftentransmitted over a communication bus/interconnect between IP blocks ofthe NOC. As the number of IP blocks and hardware threads configuredtherein continues to rise, the amount of data being communicated overthe communication bus of the NOC likewise continues to rise.Improvements in the logic of IP blocks have led to power efficientprocessing. However, moving data, i.e., communicating data packets hasnot kept pace with the power reduction improvements in conventionalsystems. In fact, in many conventional processors, more power is nowconsumed moving data than performing processing on the data.

A primary source of power consumption in association with datacommunication results from data signals transitioning between logical“1” and logical “0” values, as the CMOS logic gates typically used inmost NOC architecture systems dissipate the most power when switchingbetween logic states. Thus, as the speed of communication bus increases,and the amount of communicated data increases, the overall powerconsumption of the NOC rises accordingly.

Therefore, a continuing need exists in the art for a manner ofincreasing the efficiency of on chip communications.

SUMMARY OF THE INVENTION

The invention addresses these and other problems associated with theprior art by encoding data to be communicated over a communication busto reduce bit transitions for communications, and thereby reduce theamount of switching of logic gates in the communication bus, as well asthe associated power consumption that comes from such switching. Theencoding is based both on historical and future data communications,such that the encoding selected for a particular data value is based onboth the data transmitted prior to, and subsequent to, that data value.

In particular, embodiments of the invention selectively encode datavalues based at least in part on at least one data value queued to becommunicated thereafter and a previously communicated encoded datavalue. Each data value is encoded to a particular encoded data value ofa group of possible encoded data values that correspond to the datavalue. By encoding the data values prior to communication to reduce bittransitions in the communicated data, embodiments of the inventionreduce the switching of logic gates in the communication bus, wherereducing switching in turn reduces power consumption in the processor.

These and other advantages and features, which characterize theinvention, are set forth in the claims annexed hereto and forming afurther part hereof. However, for a better understanding of theinvention, and of the advantages and objectives attained through itsuse, reference should be made to the drawings, and to the accompanyingdescriptive matter, in which there is described exemplary embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of exemplary automated computing machineryincluding an exemplary computer useful in data processing consistentwith embodiments of the present invention.

FIG. 2 is a block diagram of an exemplary NOC implemented in thecomputer of FIG. 1.

FIG. 3 is a block diagram illustrating in greater detail an exemplaryimplementation of a node from the NOC of FIG. 2.

FIG. 4 is a block diagram illustrating an exemplary implementation of anIP block from the NOC of FIG. 2.

FIG. 5 is a block diagram of a of a communication queue and encode logicthat may be connected to a communication bus or interconnect of the NOCof FIG. 2 to encode data values prior to communication in the NOC.

FIGS. 6A-C are block diagrams including example data values that may beencoded and communicated using the encode logic of FIG. 5.

FIG. 7 provides a flowchart that illustrates a sequence of operationsthat may be performed by the encode logic of FIG. 5.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of embodimentsof the invention. The specific features consistent with embodiments ofthe invention disclosed herein, including, for example, specificdimensions, orientations, locations, sequences of operations and shapesof various illustrated components, will be determined in part by theparticular intended application, use and/or environment. Certainfeatures of the illustrated embodiments may have been enlarged ordistorted relative to others to facilitate visualization and clearunderstanding.

DETAILED DESCRIPTION

Embodiments of the invention provide a circuit arrangement and methodfor communicating data over a communication bus/interconnect. Datavalues queued to be communicated may be selectively encoded to aparticular encoded data value based at least in part on a data valuequeued to be communicated thereafter and a previously communicatedencoded data value. Each data value is encoded to the particular encodeddata value of a group of possible encoded values, where the particularencoded value reduces the number of bit transitions for communicatingthe encoded data values. By selectively encoding each data value to theparticular encoded value that reduces bit transitions, embodiments ofthe invention thereby reduce switching during communication, which inturn may reduce power consumption as compared to communicating theunencoded data values.

Hardware and Software Environment

Now turning to the drawings, wherein like numbers denote like partsthroughout the several views, FIG. 1 illustrates exemplary automatedcomputing machinery including an exemplary computer 10 useful in dataprocessing consistent with embodiments of the present invention.Computer 10 of FIG. 1 includes at least one computer processor 12 or‘CPU’ as well as random access memory 14 (‘RAM’), which is connectedthrough a high speed memory bus 16 and bus adapter 18 to processor 12and to other components of the computer 10.

Stored in RAM 14 is an application program 20, a module of user-levelcomputer program instructions for carrying out particular dataprocessing tasks such as, for example, word processing, spreadsheets,database operations, video gaming, stock market simulations, atomicquantum process simulations, or other user-level applications. Alsostored in RAM 14 is an operating system 22. Operating systems useful inconnection with embodiments of the invention include UNIX™, Linux,Microsoft Windows XP™, AIX™, IBM's i5/OS™, and others as will occur tothose of skill in the art. Operating system 22 and application 20 in theexample of FIG. 1 are shown in RAM 14, but many components of suchsoftware typically are stored in non-volatile memory also, e.g., on adisk drive 24.

As will become more apparent below, embodiments consistent with theinvention may be implemented within Network On Chip (NOC) integratedcircuit devices, or chips, and as such, computer 10 is illustratedincluding two exemplary NOCs: a video adapter 26 and a coprocessor 28.NOC video adapter 26, which may alternatively be referred to as agraphics adapter, is an example of an I/O adapter specially designed forgraphic output to a display device 30 such as a display screen orcomputer monitor. NOC video adapter 26 is connected to processor 12through a high speed video bus 32, bus adapter 18, and the front sidebus 34, which is also a high speed bus. NOC Coprocessor 28 is connectedto processor 12 through bus adapter 18, and front side buses 34 and 36,which is also a high speed bus. The NOC coprocessor of FIG. 1 may beoptimized, for example, to accelerate particular data processing tasksat the behest of the main processor 12.

The exemplary NOC video adapter 26 and NOC coprocessor 28 of FIG. 1 eachinclude a NOC, including integrated processor (‘IP’) blocks, routers,memory communications controllers, and network interface controllers,the details of which will be discussed in greater detail below inconnection with FIGS. 2-3. The NOC video adapter and NOC coprocessor areeach optimized for programs that use parallel processing and alsorequire fast random access to shared memory. It will be appreciated byone of ordinary skill in the art having the benefit of the instantdisclosure, however, that the invention may be implemented in devicesand device architectures other than NOC devices and devicearchitectures. The invention is therefore not limited to implementationwithin an NOC device.

Computer 10 of FIG. 1 includes disk drive adapter 38 coupled through anexpansion bus 40 and bus adapter 18 to processor 12 and other componentsof the computer 10. Disk drive adapter 38 connects non-volatile datastorage to the computer 10 in the form of disk drive 24, and may beimplemented, for example, using Integrated Drive Electronics (‘IDE’)adapters, Small Computer System Interface (‘SCSI’) adapters, and othersas will occur to those of skill in the art. Non-volatile computer memoryalso may be implemented for as an optical disk drive, electricallyerasable programmable read-only memory (so-called ‘EEPROM’ or ‘Flash’memory), RAM drives, and so on, as will occur to those of skill in theart.

Computer 10 also includes one or more input/output (‘I/O’) adapters 42,which implement user-oriented input/output through, for example,software drivers and computer hardware for controlling output to displaydevices such as computer display screens, as well as user input fromuser input devices 44 such as keyboards and mice. In addition, computer10 includes a communications adapter 46 for data communications withother computers 48 and for data communications with a datacommunications network 50. Such data communications may be carried outserially through RS-232 connections, through external buses such as aUniversal Serial Bus (‘USB’), through data communications datacommunications networks such as IP data communications networks, and inother ways as will occur to those of skill in the art. Communicationsadapters implement the hardware level of data communications throughwhich one computer sends data communications to another computer,directly or through a data communications network. Examples ofcommunications adapters suitable for use in computer 10 include modemsfor wired dial-up communications, Ethernet (IEEE 802.3) adapters forwired data communications network communications, and 802.11 adaptersfor wireless data communications network communications.

For further explanation, FIG. 2 sets forth a functional block diagram ofan example NOC 102 according to embodiments of the present invention.The NOC in FIG. 2 is implemented on a ‘chip’ 100, that is, on anintegrated circuit. NOC 102 includes integrated processor (‘IP’) blocks104, routers 110, memory communications controllers 106, and networkinterface controllers 108 grouped into interconnected nodes. Each IPblock 104 is adapted to a router 110 through a memory communicationscontroller 106 and a network interface controller 108. Each memorycommunications controller controls communications between an IP blockand memory, and each network interface controller 108 controls inter-IPblock communications through routers 110.

In NOC 102, each IP block represents a reusable unit of synchronous orasynchronous logic design used as a building block for data processingwithin the NOC. The term ‘IP block’ is sometimes expanded as‘intellectual property block,’ effectively designating an IP block as adesign that is owned by a party, that is the intellectual property of aparty, to be licensed to other users or designers of semiconductorcircuits. In the scope of the present invention, however, there is norequirement that IP blocks be subject to any particular ownership, sothe term is always expanded in this specification as ‘integratedprocessor block.’ IP blocks, as specified here, are reusable units oflogic, cell, or chip layout design that may or may not be the subject ofintellectual property. IP blocks are logic cores that can be formed asASIC chip designs or FPGA logic designs.

One way to describe IP blocks by analogy is that IP blocks are for NOCdesign what a library is for computer programming or a discreteintegrated circuit component is for printed circuit board design. InNOCs consistent with embodiments of the present invention, IP blocks maybe implemented as generic gate netlists, as complete special purpose orgeneral purpose microprocessors, or in other ways as may occur to thoseof skill in the art. A netlist is a Boolean-algebra representation(gates, standard cells) of an IP block's logical-function, analogous toan assembly-code listing for a high-level program application. NOCs alsomay be implemented, for example, in synthesizable form, described in ahardware description language such as Verilog or VHDL. In addition tonetlist and synthesizable implementation, NOCs also may be delivered inlower-level, physical descriptions. Analog IP block elements such asSERDES, PLL, DAC, ADC, and so on, may be distributed in atransistor-layout format such as GDSII. Digital elements of IP blocksare sometimes offered in layout format as well. It will also beappreciated that IP blocks, as well as other logic circuitry implementedconsistent with the invention may be distributed in the form of computerdata files, e.g., logic definition program code, that define at variouslevels of detail the functionality and/or layout of the circuitarrangements implementing such logic. Thus, while the invention has andhereinafter will be described in the context of circuit arrangementsimplemented in fully functioning integrated circuit devices, dataprocessing systems utilizing such devices, and other tangible, physicalhardware circuits, those of ordinary skill in the art having the benefitof the instant disclosure will appreciate that the invention may also beimplemented within a program product, and that the invention appliesequally regardless of the particular type of computer readable storagemedium being used to distribute the program product. Examples ofcomputer readable storage media include, but are not limited to,physical, recordable type media such as volatile and non-volatile memorydevices, floppy disks, hard disk drives, CD-ROMs, and DVDs (amongothers).

Each IP block 104 in the example of FIG. 2 is adapted to a router 110through a memory communications controller 106. Each memorycommunication controller is an aggregation of synchronous andasynchronous logic circuitry adapted to provide data communicationsbetween an IP block and memory. Examples of such communications betweenIP blocks and memory include memory load instructions and memory storeinstructions. The memory communications controllers 106 are described inmore detail below with reference to FIG. 3. Each IP block 104 is alsoadapted to a router 110 through a network interface controller 108,which controls communications through routers 110 between IP blocks 104.Examples of communications between IP blocks include messages carryingdata and instructions for processing the data among IP blocks inparallel applications and in pipelined applications. The networkinterface controllers 108 are also described in more detail below withreference to FIG. 3.

Routers 110, and the corresponding links 118 therebetween, implement thenetwork operations of the NOC. The links 118 may be packet structuresimplemented on physical, parallel wire buses connecting all the routers.That is, each link may be implemented on a wire bus wide enough toaccommodate simultaneously an entire data switching packet, includingall header information and payload data. If a packet structure includes64 bytes, for example, including an eight byte header and 56 bytes ofpayload data, then the wire bus subtending each link is 64 bytes wide,512 wires. In addition, each link may be bi-directional, so that if thelink packet structure includes 64 bytes, the wire bus actually contains1024 wires between each router and each of its neighbors in the network.In such an implementation, a message could include more than one packet,but each packet would fit precisely onto the width of the wire bus. Inthe alternative, a link may be implemented on a wire bus that is onlywide enough to accommodate a portion of a packet, such that a packetwould be broken up into multiple beats, e.g., so that if a link isimplemented as 16 bytes in width, or 128 wires, a 64 byte packet couldbe broken into four beats. It will be appreciated that differentimplementations may used different bus widths based on practicalphysical limits as well as desired performance characteristics. If theconnection between the router and each section of wire bus is referredto as a port, then each router includes five ports, one for each of fourdirections of data transmission on the network and a fifth port foradapting the router to a particular IP block through a memorycommunications controller and a network interface controller.

Each memory communications controller 106 controls communicationsbetween an IP block and memory. Memory can include off-chip main RAM112, memory 114 connected directly to an IP block through a memorycommunications controller 106, on-chip memory enabled as an IP block116, and on-chip caches. In NOC 102, either of the on-chip memories 114,116, for example, may be implemented as on-chip cache memory. All theseforms of memory can be disposed in the same address space, physicaladdresses or virtual addresses, true even for the memory attacheddirectly to an IP block. Memory addressed messages therefore can beentirely bidirectional with respect to IP blocks, because such memorycan be addressed directly from any IP block anywhere on the network.Memory 116 on an IP block can be addressed from that IP block or fromany other IP block in the NOC. Memory 114 attached directly to a memorycommunication controller can be addressed by the IP block that isadapted to the network by that memory communication controller—and canalso be addressed from any other IP block anywhere in the NOC.

NOC 102 includes two memory management units (‘MMUs’) 120, 122,illustrating two alternative memory architectures for NOCs consistentwith embodiments of the present invention. MMU 120 is implemented withinan IP block, allowing a processor within the IP block to operate invirtual memory while allowing the entire remaining architecture of theNOC to operate in a physical memory address space. MMU 122 isimplemented off-chip, connected to the NOC through a data communicationsport 124. The port 124 includes the pins and other interconnectionsrequired to conduct signals between the NOC and the MMU, as well assufficient intelligence to convert message packets from the NOC packetformat to the bus format required by the external MMU 122. The externallocation of the MMU means that all processors in all IP blocks of theNOC can operate in virtual memory address space, with all conversions tophysical addresses of the off-chip memory handled by the off-chip MMU122.

In addition to the two memory architectures illustrated by use of theMMUs 120, 122, data communications port 126 illustrates a third memoryarchitecture useful in NOCs capable of being utilized in embodiments ofthe present invention. Port 126 provides a direct connection between anIP block 104 of the NOC 102 and off-chip memory 112. With no MMU in theprocessing path, this architecture provides utilization of a physicaladdress space by all the IP blocks of the NOC. In sharing the addressspace bi-directionally, all the IP blocks of the NOC can access memoryin the address space by memory-addressed messages, including loads andstores, directed through the IP block connected directly to the port126. The port 126 includes the pins and other interconnections requiredto conduct signals between the NOC and the off-chip memory 112, as wellas sufficient intelligence to convert message packets from the NOCpacket format to the bus format required by the off-chip memory 112.

In the example of FIG. 2, one of the IP blocks is designated a hostinterface processor 128. A host interface processor 128 provides aninterface between the NOC and a host computer 10 in which the NOC may beinstalled and also provides data processing services to the other IPblocks on the NOC, including, for example, receiving and dispatchingamong the IP blocks of the NOC data processing requests from the hostcomputer. A NOC may, for example, implement a video graphics adapter 26or a coprocessor 28 on a larger computer 10 as described above withreference to FIG. 1. In the example of FIG. 2, the host interfaceprocessor 128 is connected to the larger host computer through a datacommunications port 130. The port 130 includes the pins and otherinterconnections required to conduct signals between the NOC and thehost computer, as well as sufficient intelligence to convert messagepackets from the NOC to the bus format required by the host computer 10.In the example of the NOC coprocessor in the computer of FIG. 1, such aport would provide data communications format translation between thelink structure of the NOC coprocessor 28 and the protocol required forthe front side bus 36 between the NOC coprocessor 28 and the bus adapter18.

FIG. 3 next illustrates a functional block diagram illustrating ingreater detail the components implemented within an IP block 104, memorycommunications controller 106, network interface controller 108 androuter 110 in NOC 102, collectively illustrated at 132 which may bereferred to as a node or a hardware thread. IP block 104 includes acomputer processor 134 and I/O functionality 136. In this example,computer memory is represented by a segment of random access memory(‘RAM’) 138 in IP block 104. The memory, as described above withreference to FIG. 2, can occupy segments of a physical address spacewhose contents on each IP block are addressable and accessible from anyIP block in the NOC. The processors 134, I/O capabilities 136, andmemory 138 in each IP block effectively implement the IP blocks asgenerally programmable microcomputers. As explained above, however, inthe scope of the present invention, IP blocks generally representreusable units of synchronous or asynchronous logic used as buildingblocks for data processing within a NOC. Implementing IP blocks asgenerally programmable microcomputers, therefore, although a commonembodiment useful for purposes of explanation, is not a limitation ofthe present invention.

In NOC 102 of FIG. 3, each memory communications controller 106 includesa plurality of memory communications execution engines 140. Each memorycommunications execution engine 140 is enabled to execute memorycommunications instructions from an IP block 104, includingbidirectional memory communications instruction flow 141, 142, 144between the network and the IP block 104. The memory communicationsinstructions executed by the memory communications controller mayoriginate, not only from the IP block adapted to a router through aparticular memory communications controller, but also from any IP block104 anywhere in NOC 102. That is, any IP block in the NOC can generate amemory communications instruction and transmit that memorycommunications instruction through the routers of the NOC to anothermemory communications controller associated with another IP block forexecution of that memory communications instruction. Such memorycommunications instructions can include, for example, translationlookaside buffer control instructions, cache control instructions,barrier instructions, and memory load and store instructions.

Each memory communications execution engine 140 is enabled to execute acomplete memory communications instruction separately and in parallelwith other memory communications execution engines. The memorycommunications execution engines implement a scalable memory transactionprocessor optimized for concurrent throughput of memory communicationsinstructions. Memory communications controller 106 supports multiplememory communications execution engines 140 all of which runconcurrently for simultaneous execution of multiple memorycommunications instructions. A new memory communications instruction isallocated by the memory communications controller 106 to a memorycommunications engine 140 and memory communications execution engines140 can accept multiple response events simultaneously. In this example,all of the memory communications execution engines 140 are identical.Scaling the number of memory communications instructions that can behandled simultaneously by a memory communications controller 106,therefore, is implemented by scaling the number of memory communicationsexecution engines 140.

In NOC 102 of FIG. 3, each network interface controller 108 is enabledto convert communications instructions from command format to networkpacket format for transmission among the IP blocks 104 through routers110. The communications instructions may be formulated in command formatby the IP block 104 or by memory communications controller 106 andprovided to the network interface controller 108 in command format. Thecommand format may be a native format that conforms to architecturalregister files of IP block 104 and memory communications controller 106.The network packet format is typically the format required fortransmission through routers 110 of the network. Each such message iscomposed of one or more network packets. Examples of such communicationsinstructions that are converted from command format to packet format inthe network interface controller include memory load instructions andmemory store instructions between IP blocks and memory. Suchcommunications instructions may also include communications instructionsthat send messages among IP blocks carrying data and instructions forprocessing the data among IP blocks in parallel applications and inpipelined applications.

In NOC 102 of FIG. 3, each IP block is enabled to sendmemory-address-based communications to and from memory through the IPblock's memory communications controller and then also through itsnetwork interface controller to the network. A memory-address-basedcommunications is a memory access instruction, such as a loadinstruction or a store instruction, that is executed by a memorycommunication execution engine of a memory communications controller ofan IP block. Such memory-address-based communications typicallyoriginate in an IP block, formulated in command format, and handed offto a memory communications controller for execution.

Many memory-address-based communications are executed with messagetraffic, because any memory to be accessed may be located anywhere inthe physical memory address space, on-chip or off-chip, directlyattached to any memory communications controller in the NOC, orultimately accessed through any IP block of the NOC—regardless of whichIP block originated any particular memory-address-based communication.Thus, in NOC 102, all memory-address-based communications that areexecuted with message traffic are passed from the memory communicationscontroller to an associated network interface controller for conversionfrom command format to packet format and transmission through thenetwork in a message. In converting to packet format, the networkinterface controller also identifies a network address for the packet independence upon the memory address or addresses to be accessed by amemory-address-based communication. Memory address based messages areaddressed with memory addresses. Each memory address is mapped by thenetwork interface controllers to a network address, typically thenetwork location of a memory communications controller responsible forsome range of physical memory addresses. The network location of amemory communication controller 106 is naturally also the networklocation of that memory communication controller's associated router110, network interface controller 108, and IP block 104. The instructionconversion logic 150 within each network interface controller is capableof converting memory addresses to network addresses for purposes oftransmitting memory-address-based communications through routers of aNOC.

Upon receiving message traffic from routers 110 of the network, eachnetwork interface controller 108 inspects each packet for memoryinstructions. Each packet containing a memory instruction is handed tothe memory communications controller 106 associated with the receivingnetwork interface controller, which executes the memory instructionbefore sending the remaining payload of the packet to the IP block forfurther processing. In this way, memory contents are always prepared tosupport data processing by an IP block before the IP block beginsexecution of instructions from a message that depend upon particularmemory content.

In NOC 102 of FIG. 3, each IP block 104 is enabled to bypass its memorycommunications controller 106 and send inter-IP block, network-addressedcommunications 146 directly to the network through the IP block'snetwork interface controller 108. Network-addressed communications aremessages directed by a network address to another IP block. Suchmessages transmit working data in pipelined applications, multiple datafor single program processing among IP blocks in a SIMD application, andso on, as will occur to those of skill in the art. Such messages aredistinct from memory-address-based communications in that they arenetwork addressed from the start, by the originating IP block whichknows the network address to which the message is to be directed throughrouters of the NOC. Such network-addressed communications are passed bythe IP block through I/O functions 136 directly to the IP block'snetwork interface controller in command format, then converted to packetformat by the network interface controller and transmitted throughrouters of the NOC to another IP block. Such network-addressedcommunications 146 are bi-directional, potentially proceeding to andfrom each IP block of the NOC, depending on their use in any particularapplication. Each network interface controller, however, is enabled toboth send and receive such communications to and from an associatedrouter, and each network interface controller is enabled to both sendand receive such communications directly to and from an associated IPblock, bypassing an associated memory communications controller 106.

Each network interface controller 108 in the example of FIG. 3 is alsoenabled to implement virtual channels on the network, characterizingnetwork packets by type. Each network interface controller 108 includesvirtual channel implementation logic 148 that classifies eachcommunication instruction by type and records the type of instruction ina field of the network packet format before handing off the instructionin packet form to a router 110 for transmission on the NOC. Examples ofcommunication instruction types include inter-IP blocknetwork-address-based messages, request messages, responses to requestmessages, invalidate messages directed to caches; memory load and storemessages; and responses to memory load messages, etc.

Each router 110 in the example of FIG. 3 includes routing logic 152,virtual channel control logic 154, and virtual channel buffers 156. Therouting logic typically is implemented as a network of synchronous andasynchronous logic that implements a data communications protocol stackfor data communication in the network formed by the routers 110, links118, and bus wires among the routers. Routing logic 152 includes thefunctionality that readers of skill in the art might associate inoff-chip networks with routing tables, routing tables in at least someembodiments being considered too slow and cumbersome for use in a NOC.Routing logic implemented as a network of synchronous and asynchronouslogic can be configured to make routing decisions as fast as a singleclock cycle. The routing logic in this example routes packets byselecting a port for forwarding each packet received in a router. Eachpacket contains a network address to which the packet is to be routed.

In describing memory-address-based communications above, each memoryaddress was described as mapped by network interface controllers to anetwork address, a network location of a memory communicationscontroller. The network location of a memory communication controller106 is naturally also the network location of that memory communicationcontroller's associated router 110, network interface controller 108,and IP block 104. In inter-IP block, or network-address-basedcommunications, therefore, it is also typical for application-level dataprocessing to view network addresses as the location of an IP blockwithin the network formed by the routers, links, and bus wires of theNOC. FIG. 2 illustrates that one organization of such a network is amesh of rows and columns in which each network address can beimplemented, for example, as either a unique identifier for each set ofassociated router, IP block, memory communications controller, andnetwork interface controller of the mesh or x, y coordinates of eachsuch set in the mesh.

In NOC 102 of FIG. 3, each router 110 implements two or more virtualcommunications channels, where each virtual communications channel ischaracterized by a communication type. Communication instruction types,and therefore virtual channel types, include those mentioned above:inter-IP block network-address-based messages, request messages,responses to request messages, invalidate messages directed to caches;memory load and store messages; and responses to memory load messages,and so on. In support of virtual channels, each router 110 in theexample of FIG. 3 also includes virtual channel control logic 154 andvirtual channel buffers 156. The virtual channel control logic 154examines each received packet for its assigned communications type andplaces each packet in an outgoing virtual channel buffer for thatcommunications type for transmission through a port to a neighboringrouter on the NOC.

Each virtual channel buffer 156 has finite storage space. When manypackets are received in a short period of time, a virtual channel buffercan fill up—so that no more packets can be put in the buffer. In otherprotocols, packets arriving on a virtual channel whose buffer is fullwould be dropped. Each virtual channel buffer 156 in this example,however, is enabled with control signals of the bus wires to advisesurrounding routers through the virtual channel control logic to suspendtransmission in a virtual channel, that is, suspend transmission ofpackets of a particular communications type. When one virtual channel isso suspended, all other virtual channels are unaffected—and can continueto operate at full capacity. The control signals are wired all the wayback through each router to each router's associated network interfacecontroller 108. Each network interface controller is configured to, uponreceipt of such a signal, refuse to accept, from its associated memorycommunications controller 106 or from its associated IP block 104,communications instructions for the suspended virtual channel. In thisway, suspension of a virtual channel affects all the hardware thatimplements the virtual channel, all the way back up to the originatingIP blocks.

One effect of suspending packet transmissions in a virtual channel isthat no packets are ever dropped. When a router encounters a situationin which a packet might be dropped in some unreliable protocol such as,for example, the Internet Protocol, the routers in the example of FIG. 3may suspend by their virtual channel buffers 156 and their virtualchannel control logic 154 all transmissions of packets in a virtualchannel until buffer space is again available, eliminating any need todrop packets. The NOC of FIG. 3, therefore, may implement highlyreliable network communications protocols with an extremely thin layerof hardware.

The example NOC of FIG. 3 may also be configured to maintain cachecoherency between both on-chip and off-chip memory caches. Each NOC cansupport multiple caches each of which operates against the sameunderlying memory address space. For example, caches may be controlledby IP blocks, by memory communications controllers, or by cachecontrollers external to the NOC. Either of the on-chip memories 114, 116in the example of FIG. 2 may also be implemented as an on-chip cache,and, within the scope of the present invention, cache memory can beimplemented off-chip also.

Each router 110 illustrated in FIG. 3 includes five ports, four ports158A-D connected through bus wires 118 to other routers and a fifth port160 connecting each router to its associated IP block 104 through anetwork interface controller 108 and a memory communications controller106. As can be seen from the illustrations in FIGS. 2 and 3, the routers110 and the links 118 of the NOC 102 form a mesh network with verticaland horizontal links connecting vertical and horizontal ports in eachrouter. In the illustration of FIG. 3, for example, ports 158A, 158C and160 are termed vertical ports, and ports 158B and 158D are termedhorizontal ports.

FIG. 4 next illustrates in another manner one exemplary implementationof an IP block 104 consistent with the invention, implemented as aprocessing element partitioned into an instruction unit (IU) 162,execution unit (XU) 164 and auxiliary execution unit (AXU) 166. In theillustrated implementation, IU 162 includes a plurality of instructionbuffers 168 that receive instructions from an L1 instruction cache(iCACHE) 170. Each instruction buffer 168 is dedicated to one of aplurality, e.g., four, symmetric multithreaded (SMT) hardware threads.An effective-to-real translation unit (iERAT) 172 is coupled to iCACHE170, and is used to translate instruction fetch requests from aplurality of thread fetch sequencers 174 into real addresses forretrieval of instructions from lower order memory. Each thread fetchsequencer 174 is dedicated to a particular hardware thread, and is usedto ensure that instructions to be executed by the associated thread isfetched into the iCACHE for dispatch to the appropriate execution unit.As also shown in FIG. 4, instructions fetched into instruction buffer168 may also be monitored by branch prediction logic 176, which provideshints to each thread fetch sequencer 174 to minimize instruction cachemisses resulting from branches in executing threads.

IU 162 also includes a dependency/issue logic block 178 dedicated toeach hardware thread, and configured to resolve dependencies and controlthe issue of instructions from instruction buffer 168 to XU 164. Inaddition, in the illustrated embodiment, separate dependency/issue logic180 is provided in AXU 166, thus enabling separate instructions to beconcurrently issued by different threads to XU 164 and AXU 166. In analternative embodiment, logic 180 may be disposed in IU 162, or may beomitted in its entirety, such that logic 178 issues instructions to AXU166.

XU 164 is implemented as a fixed point execution unit, including a setof general purpose registers (GPR's) 182 coupled to fixed point logic184, branch logic 186 and load/store logic 188. Load/store logic 188 iscoupled to an L1 data cache (dCACHE) 190, with effective to realtranslation provided by dERAT logic 192. XU 164 may be configured toimplement practically any instruction set, e.g., all or a portion of a32 b or 64 b PowerPC instruction set.

AXU 166 operates as an auxiliary execution unit including dedicateddependency/issue logic 180 along with one or more execution blocks 194.AXU 166 may include any number of execution blocks, and may implementpractically any type of execution unit, e.g., a floating point unit, orone or more specialized execution units such as encryption/decryptionunits, coprocessors, vector processing units, graphics processing units,XML processing units, etc. In the illustrated embodiment, AXU 166includes a high speed auxiliary interface to XU 164, e.g., to supportdirect moves between AXU architected state and XU architected state.

Communication with IP block 104 may be managed in the manner discussedabove in connection with FIG. 2, via network interface controller 108coupled to NOC 102. Address-based communication, e.g., to access L2cache memory, may be provided, along with message-based communication.For example, each IP block 104 may include a dedicated in box and/or outbox in order to handle inter-node communications between IP blocks.

Embodiments of the present invention may be implemented within thehardware and software environment described above in connection withFIGS. 1-4. However, it will be appreciated by one of ordinary skill inthe art having the benefit of the instant disclosure that the inventionmay be implemented in a multitude of different environments, and thatother modifications may be made to the aforementioned hardware andsoftware embodiment without departing from the spirit and scope of theinvention. As such, the invention is not limited to the particularhardware and software environment disclosed herein.

Chip Level Encoded Data Communications

Turning now to FIG. 5, this figure provides a block diagram illustratingcomponents that may be configured in the NOC 102, IP block 104 and/orrouter 110 of FIG. 2. As shown, a communication queue 202 may store datavalues 204 a-c (also labeled ‘DATA VALUE X’ through ‘DATA VALUE X+N’)that are queued for communication over a connected communication bus206. In general, the ‘DATA VALUE X’ 204 a corresponds to a first datavalue that is to be communicated over the communication bus 206, and‘DATA VALUE X+1’ 204 b through ‘DATA VALUE X+N’ 204 c corresponds todata values queued to be communicated after the first data value 104 a.The communication queue 202 is connected to encode logic 208, where theencode logic may be associated with a memory that stores encoded values210 a,b (also labeled ‘ENCODED VALUE X-1’ through ‘ENCODED VALUE X-N’)that were previously communicated over the communication bus 206.Consistent with embodiments of the invention, the encode logic 208 maybe connected to the communication queue 202 and/or the communication bus206, and the encode logic 208 may be configured to encode data values(e.g., DATA VALUE X 206 a) prior to communication based at least in parton one or more previously communicated encoded values 210 a, b and oneor more data values queued to be communicated thereafter 204 b,c.

Consistent with embodiments of the invention, the encode logic 208 mayanalyze one or more previously communicated encoded values 210 a,b andone or more data values 204 b,c queued to be communicated after thefirst data value 206 a and determine an encoded value for the first datavalue 204 a, and in some embodiments, also determine an encoded valuefor a subsequent data value 204 b such that bit transitions are reducedin communicating the first data value 204 a and at least one other datavalue 204 b queued to be communicated thereafter. In general, a datavalue may be encoded by the encode logic 208 to a particular encodedvalue from a group of possible encoded values prior to communication onthe communication bus 206. As such, in embodiments of the invention, theencode logic analyzes the first data value 204 a, one or more previouslycommunicated encoded values 210 a,b, and one or more data values queuedto be communicated thereafter 210 a,b to determine a particular encodedvalue from the group of possible encoded values for the first data value204 a. The encode logic 208 encodes the first data value 206 a togenerate the particular encoded value, and the particular encoded valuemay be communicated over the communication bus 206.

The encode logic 208 may include transition count logic 212 that isconfigured to determine the number of bit transitions between at leastone previously communicated encoded value 210 a, each possible encodedvalue for the first value 204 a and/or each possible encoded value forat least one data value 204 b queued to be communicated after the firstdata value 204 a. For example, the transition count logic 212 mayinclude ‘exclusive or’ (XOR) logic that compares each bit of eachpossible encoded value for the first data value 204 a to a correspondingbit in the previously communicated encoded value 210 a and acorresponding bit in each possible encoded value for a subsequentlyqueued data value 204 b to determine a number of bit transitions foreach comparison. Based at least in part on the determined number of bittransitions for each possible encoded value for the first data value 204a, previously communicated encoded value 210 a, and each possibleencoded value for the subsequently queued data value 204 b, the encodelogic 208 encodes the first data value 204 a to a particular encodedvalue from the group of possible encoded values.

FIGS. 6A-C provides block diagrams of the communication queue 202 andencode logic 208 including an example value for the first data value 204a ‘00000000’, a subsequently queued data value (i.e., a second datavalue) 204 b ‘10100101’, and a previously communicated encoded value 210a ‘0000000000’. Turning to FIG. 6A, in this example, the encode logic208 is configured to perform 8/10 encoding on the first data value 204 aand the second data value 204, where the 8/10 encoding may encode each 8bit data value 204 a,b into any of four possible encoded values of 10bits. In this example, the first data value 204 a may be encoded using8/10 encoding to generate four 10 bit possible encoded values 220 a-d,and the second data value 104 b may be encoded using 8/10 encoding togenerate four 10 bit possible encoded values 222 a-d.

As discussed, in some embodiments of the invention the transition countlogic 212 may analyze each possible encoded value of the first datavalue 204 a and the previously communicated encoded value 210 a todetermine the number of bit transitions for each possible encoded valueand the previously communicated encoded value 210 a. As shown in FIG.6B, the transition count logic 212 may compare each bit of thepreviously communicated encoded value 210 a to each possible encodedvalue 220 a-d of the first data value 204 a to determine the number ofbit transitions 240 a-d between the previously communicated encodedvalue 210 a and each possible encoded value 220 a-d for the first datavalue 204 a. Thus, as shown in FIG. 6B, for an encoded value 220 a of“0000000000” for the first data value, the number of transitions fromthe previously communicated value of “0000000000” is zero, since thenumbers are identical. However, for the encoded values 220 b, 200 c of“1111100000” and “0000011111”, the number of transitions is five, sincefive bits are switched from“0” to “1”. Likewise, for the encoded value220 d of “1111111111”, the number of transitions is ten, since all tenbits are switched from “0” to “1”.

Moreover, the transition count logic 212 may be configured to determinethe number of bit transitions between each possible encoded value forthe first data value 204 a and each possible encoded value for thesecond data value 204 b (since, at this point, the encoded value for thesecond data value has not yet been determined). In FIG. 6C, thetransition count logic 212 may compare each bit of a first possibleencoded value 220 a for the first data value 204 a to corresponding bitsof each possible encoded value for the second data value 204 b todetermine the number of bit transitions 242 a-d therebetween. Thetransition count logic 212 performs a similar analysis to determine: thenumber of bit transitions 244 a-d between a second possible encodedvalue 220 b of the first data value 204 a and each possible encodedvalue 222 a-d of the second data value 204 b, the number of bittransitions 246 a-d between a third possible encoded value 220 c of thefirst data value 204 a and each possible encoded value 222 a-d of thesecond data value 204 b, and the number of bit transitions 248 a-dbetween a fourth possible encoded value 220 d of the first data value204 a and each possible encoded value 222 a-d of the second data value204 b.

Based on the determined number of bit transitions 240 a-d between thepreviously communicated encoded value 210 a and the possible encodedvalues 220 a-d for the first data value 204 a shown in FIG. 6B, and thedetermined number of bit transitions 242 a-d, 244 a-d, 246 a-d, 248 a-dbetween each possible encoded value 220 a-d of the first data value 204a and each possible encoded value 222 a-d of the second data value 204b, the encode logic 208 may encode the first data value 204 a to aparticular encoded value of the possible encoded values 220 a-d suchthat a predicted minimum number of bit transitions may performed whencommunicating the particular encoded value of the first data value 204 aand subsequent data values over the communication bus 206. Moreover,after encoding the first data value 204 a, the encode logic 208 mayencode the second data value 204 b to a particular encoded value of thepossible encoded values 222 a-d such that the minimum number of bittransitions may be performed when communicating the particular encodedvalue of the second data value 204 b over the communication bus 206. Inthis example, the encode logic may encode the first data value 204 a tothe first possible encoded value 220 a because the predicted bittransitions 240 a would be zero between the previously communicatedencoded value 210 a and the predicted bit transitions between the firstpossible encoded value 220 a and the possible encoded values 222 a-d forthe second value includes a possibility for the lowest number of bittransitions 242 a (i.e., 4).

In general, embodiments of the invention selectively encode the firstdata value and subsequent data values based on a predicted number of bittransitions. However, the communication queue 202 is continuouslyloading new data values, such that the encode logic 208 is continuouslyanalyzing and determining the number of bit transitions for the possibleencoded values for queued data value. As such, the encode logicgenerally encodes a data value to a particular encoded value based onthe predicted number of bit transitions for the loaded data values. Forexample, while the possible encoded value 222 a for the second datavalue 204 b corresponds to the lowest number of bit transitions 242 a,the encode logic may not necessarily encode the second data value 204 bto the possible encoded value 222 a corresponding to the lowest numberof bit transitions if a number of bit transitions for a possible encodedvalue for a data value queued after the second data value would performless bit transitions if a different possible encoded value 222 b-d isused. Hence, the encode logic 208 is continuously analyzing anddetermining the number of bit transitions for possible encoded values asthe communication queue 202 loads new data values for communication, andthe encode logic 208 selectively encodes data values prior tocommunication based on the current state of the communication queue 202and a previously communicated encoded value 210 a.

FIG. 7 provides a flowchart 300 that provides a sequence of operationsthat may be performed by embodiments of the invention when communicatingdata values over a communication bus and/or interconnect. Encoding logicmay be connected to a communication queue that is connected to acommunication bus/interconnect, and the encoding logic and may analyzedata values stored in a communication queue as well as a previouslycommunicated encoded value to encode the data values prior tocommunicating the data values over the communication bus to reduce thenumber of bit transitions in the communications.

Particularly, the encoding logic may analyze a data value queued to becommunicated (i.e., ‘DATA VALUE X’, a first data value) a data valuequeued to be communicated after the first data value (i.e., ‘DATA VALUEX+1’, a second data value) and an encoded value that was communicatedbefore the first data value (i.e., a communicated encoded value) (block302) to determine possible encoded values for the first and second datavalues (block 304). Furthermore, the encoding logic may determine thenumber of bit transitions between the previously communicated encodedvalue and each possible encoded value of the first data value, and alsobetween each possible encoded value of the first data value and eachpossible encoded value of the second data value (block 306).

Based at least in part on the determined bit transitions, the encodelogic may encode the first data value to a particular encoded value ofthe possible encoded values for the first data value (block 308). Ingeneral, the encode logic encodes the first data value to the particularencoded value such data may be communicated over the communication buswith the minimum number of bit transitions. Hence, the encode logicdetermines the number of bit transitions between the previouslycommunicated encoded value and the possible encoded values of the firstdata value as well as the bit transitions between each possible encodedvalue of the first data value and each possible encoded value of thesecond data value, and the first data value is encoded to the particularencoded value based at least in part on the determined number of bittransitions. The encoded value for the first data value may becommunicated (block 310), and the process may repeat for the next datavalue in the communication queue (block 312).

As such, embodiments of the invention encode data values prior tocommunicating the data values over a communication bus or interconnect.For example, embodiments of the invention may perform 8/10 encoding tothereby encode 8 bits of a data value to a 10 bit encoded value andcommunicated the encoded value over the communication bus and/orinterconnect. In general, each data value is associated with a pluralityof possible encoded values, and the data value is encoded to aparticular encoded value based at least in part on the encoded valuecommunicated before the data value and the data value queued to becommunicated thereafter. Embodiments of the invention encode each datavalue to a particular encoded value of the plurality of possible encodedvalues based at least in part on the number of bit transitions thatwould be performed communicating each possible encoded value as well aspossible subsequent encoded values. By selectively encoding data valuesprior to communication based on at least one subsequently queued datavalue and a previously communicated data value, embodiments of theinvention may thereby reduce transistor switching in communication logicconfigured in a processing system, such as a system on a chip processingunit that incorporates a NOC architecture. Reducing transistorswitching, in turn may reduce power consumption in communicating thedata values in the processing system as compared to communicating thedata values without encoding.

Therefore, embodiments of the invention selectively encode a data valueto a particular encoded value that corresponds to a low number of bittransitions and/or the minimum number of bit transitions relative to theother possible encoded values. However, since embodiments of theinvention look ahead to subsequently queued data values, a queued datavalue may be encoded to a particular data value that does not correspondto the minimum number of bit transitions relative to the other possibleencoded values but rather corresponds to a lower number of bittransitions when analyzing the possible encoded values of subsequentlyqueued data values. By selectively encoding data values prior tocommunication to a particular encoded value from a group of possibleencoded values that corresponds to the lowest number of bit transitionswhen communicating the encoded data values. As data values may becontinuously communicated from the communication queue, embodiments ofthe invention analyze a first data value and one or more subsequentlyqueued data values as well as a previously communicated encoded value(e.g., a last encoded value communicated) to determine the particularencoded values that the data values should be encoded to such that bittransitions are minimized. However, as the communication queue isgenerally loading new data values when data values are communicated, theminimum number of bit transitions may not be achieved, but ratherembodiments of the invention encode the data values to lower the numberof bit transitions when communicating the data values.

It will be appreciated that while 8/10 encoding is used in theillustrated embodiments, the invention may be used in connection withother widths of unencoded and/or encoded values where an unencoded valuemay be represented by more than one encoded value. Therefore, theinvention is not limited to the particular encoding algorithm discussedherein.

Additional advantages and modifications will readily appear to thoseskilled in the art. Thus, the invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. In particular,any of the blocks of the above flowcharts may be deleted, augmented,made to be simultaneous with another, combined, or be otherwise alteredin accordance with the principles of the invention. Accordingly,departures may be made from such details without departing from thespirit or scope of applicants' general inventive concept.

1. A method for communicating data in a system on a chip comprising a plurality IP blocks in communication over a bus, the method comprising: determining four possible encoded values for a first data value queued to be communicated over the bus and four possible encoded values for a second data value queued to be communicated after the first data value, wherein the first and second data values are 8 bits and the encoded values are 10 bits; determining a number of bit transitions between each of the four possible encoded values for the first data value and an encoded value that was previously communicated over the bus; determining a number of bit transitions between each of the four possible encoded values for the first data value and the four possible encoded values for the second data value; encoding the first data value to a particular encoded value of the four possible encoded values for the first data value using 8/10 encoding, wherein the particular encoded value corresponds to the lowest number of bit transitions between the previously communicated encoded value and the four possible encoded values for the second data value; and communicating the particular encoded value over the bus.
 2. A method for communicating data, the method comprising: selectively encoding data values for communication based at least in part on at least one data value queued to be communicated thereafter and at least one previously communicated encoded data value to reduce bit transitions for communication of the encoded data values; and communicating the selectively encoded data values.
 3. The method of claim 2, wherein selectively encoding data values for communication comprises: encoding each data value to a particular encoded data value of a group of possible encoded values for the data value, wherein the particular encoded data value corresponds to a lowest number of bit transitions between the particular encoded data value, the previously communicated encoded data value and a possible encoded data value of a data value queued to be communicated thereafter.
 4. The method of claim 3, wherein selectively encoding data values comprises: determining a number of bit transitions between each possible encoded data value of the data value and each possible encoded data value of the at least one data value queued to be communicated thereafter.
 5. The method of claim 4, wherein selectively encoding data values comprises: determining a number of bit transitions between each possible encoded data value of the data value and the previously communicated encoded data value.
 6. The method of claim 5, wherein selectively encoding data values comprises: encoding each data value to a particular encoded data value of a group of possible encoded data values associated with the data value based at least in part on the number of bit transitions between the particular encoded data value and a possible encoded value of the at least one data value queued to be communicated thereafter and the number of bit transitions between the particular encoded data value and the previously communicated encoded data value.
 7. The method of claim 2, wherein the data values comprise 8 bits, and selectively encoding data values comprises: encoding each 8 bit data value to a 10 bit encoded data value, wherein each 8 bit data value corresponds to four possible 10 bit encoded data values.
 8. The method of claim 2, further comprising: storing each encoded data value in a memory corresponding to previously communicated encoded data values responsive to communicating the encoded data value.
 9. The method of claim 2, wherein the data values are communicated between interconnected IP blocks of a system on a chip. 10.-19. (canceled) 